Web Forms :: Set Treeview Target To A Contentplaceholder In MasterPage

I have dynamically built my treeview by reading hierarchical data from database, I have divided my MasterPage like so:

<table width="100%">
<tr>
<td style="width:20%">
<asp:TreeView ID="root" Visible="true" runat="server" RootNodeStyle-ForeColor="BlueViolet">
</asp:TreeView>
</td>
<td>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server"></asp:ContentPlaceHolder>
</td>
</tr>
</table>

When I click on one of my treenode, I need to set the node.target to the "ContentPlaceHolder1", ie, keep the tree menu as still and let the content page displayed at the right part of the page. However, the node doesn't seem to recognize the ContentPlaceHolder1.

2. I have tried using <frameset> with 2<frame> pages, this way, the node.target can recognize the frame id, code as below:

<frameset cols="25%, *">
<frame src="menu.aspx" name="Menu"></frame>
<frame src="Main.aspx" name="Content"></frame>
</frameset>

But, I need to check user's login permission, I did it with session("userId") variable and I ran into a problem that the session will only exists on the left frame(menu.aspx), not the content page(Main.aspx). I have tried both methods, but one way or the other, there is some function that I cannot accomplish.